As noted herein before, Distamycin is produced from the fermentation of the mycelium of Streptomyces distallicus, and higher analogues bearing a greater number of pyrrole units are described to be prepared by semisynthesis starting from Distamycin itself obtained from the fermentation, following cumbersome chemical processes. It is clear that such a biotechnological process requires specialized equipments, apparatuses, and personnel which not always are easily available in a standard chemical industry, usually equipped with general use chemical reactors. Moreover, the producing microrganism strain and production technology have not been disclosed and the art is still a corporate know-how of the company which discovered Distamycin.
Accordingly, a number of total syntheses of Distamycin have been accomplished. Apart from small variations, the majority of the syntheses disclosed in the art utilize the key intermediate 1-methyl-4-nitro-2-pyrrolecarboxylic acid of formula (III):
(or its chemical equivalent 1-methyl-4-nitro-2-trichloacetylpyrrole) to obtain nitropyrrolecarboxyamide or aminopyrrolecarboxyamide intermediates of general formula (IV):
wherein: R1 is NO2 or NH2, R2 is alcoxy or NH—CH2CH2CN, and m is 1 or 2, by repeatedly alternating the catalytic hydrogenation step of the 4-nitro group with the acylation step of the resulting amino group with a suitable acylating derivative of the compound of formula (III), [F. Arcamone, et al., Gazz. Chim. Ital. 97:1110 (1967); M. Bialer, et al., Tetrahedron 34:2389 (1978); J. W. Lown, et al., J. Org. Chem. 50:3774 (1985); M. Shibuya, et al., Heterocycles, 27:1945 (1988)].
It is evident that the above processes require three catalytic hydrogenation steps of the nitro group, i.e. as many as the number of pyrrole rings of Distamycin. It is also evident that the number of the above mentioned hydrogenation steps will inevitably increase following increasing in the number of methylpyrrole rings, when there is provided the preparation of higher homologues of Distamycin of formula (Ia, n≧2) which, as noted herein before, show improved and more interesting bioactivities, affecting the economy and viability of the synthetic process.
Moreover, the above mentioned syntheses imply the introduction of the formyl group onto the amino group of the N-terminus moiety of the compounds of formula (Ib) at the completion of the assemblage of the required pyrrole rings. It is known in the literature and in the art that the N-formylation reaction of amidine-compounds of formula (Ib) is a troublesome, or at least unsatisfactory, process to accomplish, above all in the case of the preparation of higher analogues of Distamycin bearing a greater number of pyrrole units.
Synthetic alternatives directed to reduce the number of catalytic hydrogenation steps of the nitro group, and to avoid the introduction of the formyl group onto the amino group of the N-terminus moiety at the completion of the assemblage of the required pyrrole rings, extensively utilized both uncommon reagents and protective groups, such as those typically used for coupling reactions in the peptide chemistry, as well as column chromatography for the purification of a number of intermediates thereon, rendering the overall synthetic process poorly viable and scalable [Grehn, L., et al., J. Org. Chem. 46:3492 (1981)].
Moreover, all the above mentioned syntheses entail the transformation reaction of the C-terminus nitrile group in the C-terminus amidine group sinner reaction) at the completion of the assemblage of the required pyrrole rings.
Therefore, it is evident that there are no state-of-the-art synthetic alternatives, from the point of view of process viability, economy and scalability, to the biotechnological production of Distamycin and, more generally, to the production of poly-(4-aminopyrrole-2-carboxamide) compounds of general formula (I).
The present inventor intends to get round the disadvantages inherent to the above mentioned total syntheses of distamycin and, in general, of poly-(4-aminopyrrole-2-carboxamide) compounds of general formula (I), by using repeatedly and subsequently the intermediate 1-methyl-4-formylamino-2-pyrrolecarbonyl chloride of formula (II) in iterative alternating acylation—deformylation steps to assembly the polypyrrolecarboxamide backbone.
The compound of formula (II), so far not yet disclosed, turned to be surprisingly stable and, in the same time, chemically reactive to allow the polymerisation of the same under suitably controlled conditions to obtain the assemblage of the polypyrrolecarboxamide backbone of the desired length, avoiding the number of catalytic hydrogenation steps of the nitro group and the unsatisfactory introduction of the formyl group at the end of the pyrrolecaboxamide backbone assemblage in the case of the preparation of compounds of formula (Ia).
Therefore, the present invention provides a total synthetic process to make distamycin and, more generally, the poly-(4-aminopyrrole-2-carboxamide) compounds of general formula (I), which is more economical and alternative with respect to both the biotechnological production of distamycin (including analogues and intermediates thereof obtained by semisynthesis from fermented distamycin) and the total syntheses of the compounds of formula (I) known in the art.
According to a first aspect of the present invention, the formyl group which serves as a protecting group of the amine group at the N-terminus during the course of the synthetic process, will be present, if desired, as the functional group characterizing the final product of general formula (Ia).
A further aspect of the present invention is, therefore, a process for the manufacture of the compounds of formula (Ia), as above described; which process does not entail the formylation of the amine group at the N-terminus moiety of the corresponding compounds of formula (Ib).
A further aspect of the present invention is, therefore, a process for the manufacture of the compounds of formula (Ib), as above described, by deformylating the corresponding compounds of formula (Ia), as above described.